Reclamation process



Patented 'Aug. 14, 1945 RECLAMATION PROCESS Wilbur L. non, Hollywood, m., minor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application December 8, 1942, Serial No. 468,288

2 Claims.

This invention relates to a reclamation process and more particularly to a process for recovering defectively plated or spotted quartz crystals.

In one stage in the manufacture of quartz crystals to be used as frequency control devices in electric communication apparatus, it is sometimes the practice to provide the crystal with a spot of metallic paste to form an anchor to which lead wires may be subsequently soldered. The crystal may also be provided with a thin metallic plating. Occasionally, a defect occurs in the spot, or in the plating, and less frequently in the lead wires, and it is then desirable to remove the spot, the plating and the lead wires, and to recover the crystal which may then be reprocessed.

An object of the present invention is to provide an effective and efficient process for recovering defectively plated or spotted quartz crystals.

In accordance with one embodiment of this invention, defective crystals are immersed in a heated bath of concentrated nitric acid to which is gradually added concentrated hydrochloric acid to form aqua regia. The crystals are then rinsed in water and the operation may be repeated. The crystals are then immersed in a strong ammonium hydroxide solution, rinsed in concentrated hydrochloric acid and finally rinsed again in water.

Other objects and advantages of the present invention will be more apparent from the following detailed description.

Removal of metal from metal coated objects is ordinarily a relatively simple matter involving merely the use of the proper solvent. However, where the coating does not comprise a sin gle metal, but rather a number of metals or metallic compounds fused and pressed into the surface of a quartz crystal, the surface of which may have been previously roughened in an etching operation, removal is infinitely more difiicult.

As aforesaid, in the manufacture of quartz frequency control crystals, a spot of metallic paste is applied to the crystal. This spot may comprise suspended tin, silver, bismuth and lead metaborate particles in a binder of balsam. The paste is applied to the crystal, dried, pressed and baked at a high temperature to reduce the metals and to fuse the lead metaborate which then form a glass-like binder, trapping within it substantial amounts of these metals. The crystal may also be provided with a plating of metallic silver. Lead wires are then soldered to either side of the crystal and the crystal is tested for defects. Crystals having defects in the quartz itself are rejected and discarded. However, with crystals having defects other than imperfections in the quartz, it is desirable, as a matter of economy of manufacture to remove the lead wires, solder, spots, and plating and to recover the crystals which may then be respotted, replated and again provided with lead wires.

The salvage of quartz crystals having defects other than imperfections of the quartz itself is made possible by chemically stripping the solder leads, the silver plating and the spots described above from the crystals. While this invention will be described in connection with reclaiming a lot comprising approximately crystals, spotted and plated as above described, and of a size on the order of .4" square, it will be understood that this is merely illustrative of but one embodiment of the invention, which is to be limited only by the appended claims.

Assuming that a lot comprising 100 defective crystals is to be reclaimed, the defective crystals are placed in a container, such as a c. c. Pyrex beaker, and the container placed on a suitable heating device. Approximately 20 c. c. of concentrated nitric acid are then added to the crystals to combine with the silver, solder and bismuth, thenitric acid being maintained at a temperature of approximately 100 F. to expedite the reaction. The followin equations are illustrative of the reaction:

The stannic acid, which is the first 0r intermediate product formed, by the action of nitric acid on the tin, is further oxidized due'to an excess of available nitric acid to give stannic nitrate which is then hydrolized to give metastannic acid which settles in the nitric acid. The formation of stannic nitrate from tin and nitric acid is represented by the third equation above. The nitric acid attacks the exposed metals and dissolves them, and leaves substantially only the lead metaborate and the metals trapped therein.

Ten 0. c. of concentrated hydrochloric acid are then added to the nitric acid in the container to form aqua regia and the acid boiled for approximately three minutes. The following equations are illustrative of the reactions that then occur:

It will be apparent irom the above equations that the glass spot which comprises the lead metabcrate is decomposed by the hydrochloric acid to form lead chloride and boron chloride which are soluble in the aqua regia. At the same time metals which are trapped in the lead metaborate are released and attacked by the aqua regia. The silver nitrate in solution forms silver chloride which is largely precipitated. However, some silver chloride will adhere to the crystal because of the roughened surface and further treatment is required to remove it. The aqua regia also serves to cleanse the crystals of any oil or dirt.

The crystal is then rinsed several times in water and the process so far described may be repeated if desired, including the rinsing. By this time substantially all oi the metals and the lead metaborate glass will have been decomposed and the residue will have settled in the beaker. However, a white spot of the silver chloride will remain on the center of the crystals. This is removed by treating the crystals with 20 c. c. of strong ammonium hydroxide, the silver chloride being readily soluble therein. The following equation is illustrative of the reaction:

The crystals are then rinsed several times in distilled water to remove all traces of the reagents.

At all stages of the process meticulous care must be taken to avoid contamination, and particularly in the last rinse. A treatment in a bath of hydrochloric acid may be used before final rins- While but one embodiment 01' this invention has been described, it will be understood that many changes and modifications may be made therein without departing from the spirit or scope of the present invention.

What is claimed is:

l. A process for reclaiming a quartz crystal having a coating thereon containing tin, silver, bismuth and lead metaborate comprising treating the crystal in a bath of nitric acid, adding hydrochloric acid to the bath to form aqua regia, rinsing the crystal, treating the crystal in a bath of ammonium hydroxide, and again rinsing the crystal.

2. A process for reclaiming a quartz crystal having a coating thereon containing tin, silver, bismuth and lead metaborate comprising treating the crystal in a bath or nitric acid, adding hydrochloric acid to the bath to form aqua regia, rinsing the crystal, treating the crystal in a bath of ammonium hydroxide, treating the crystal in a bath of hydrochloric acid, and again rinsing the crystal.

WILBUR L HOFF. 

